It's worth remembering for anyone who gives RHCP a hard time regarding Stadium Arcadium (whether its deserved or not - I'm remaining neutral) that the following album, I'm With You, was almost the same format.
The 17 additional songs they recorded in those sessions were released separately from the album, but could well have been included.
RHCP at their best, ripping the funk out of a high bpm tune, just doesn't get any better, but they can't all be like that. Rough with the smooth I say and more material is better than none.
I've listened to Black Summer a few times today and it's definitely growing on me.